Position sensors are included in various systems, devices, and environments. Moreover, various types of position sensors have been developed for inclusion into these various systems, devices, and environments. One particular genre of position sensor that has been developed is the transformer position sensor. A transformer position sensor typically includes a primary or excitation coil, a secondary or output coil, and a movable magnetically permeable core. When the excitation coil is electrically excited with an excitation signal, the output coil is inductively coupled to the excitation coil and supplies an output signal that is based on the position of the movable core. One particularly popular type of transformer position sensor is the variable differential transformer position sensor, which includes linear variable differential transformers (LVDTs) and rotary variable differential transformers (RVDTs). A variable differential transformer position sensor also includes an excitation coil, an output coil, and a movable magnetically permeable core. However, with variable differential transformer position sensors either the excitation coil or the output coil is configured as a pair of differentially wound coils that are electrically coupled in series.
The transformer position sensors described above are generally reliable and robust, but do suffer certain drawbacks. For example, the magnetic permeability of the core, and thus the inductive coupling of the excitation and output coils, varies considerably with temperature. Moreover, above a certain temperature, known as the Curie temperature, the core loses its magnetic properties altogether. Although various air-core transformer position sensors have been developed to alleviate the variations in core magnetic permeability with temperature, these sensors also suffer drawbacks. In particular, presently known air-core transformer position sensors rely on movable coils that are electrically connected to external circuitry, which can increase overall complexity.
Hence, there is a need for a transformer-type position sensor that is less sensitive to variations in the inductive coupling of the excitation and output coils with temperature and/or that does not rely on moving electrical connections. The present invention addresses one or more of these needs.